The present invention generally relates to switches. In particular, the present invention relates to flow switches which are useful as a component of a high pressure washing system and other systems where the flow or stoppage of flow can be used to trigger an action.
In high pressure washing systems, water is heated in water heater tanks by burners. The burners must be regulated so that the water does not become too hot, otherwise the water heater tanks can be in danger of exploding. In the past, one method of regulating the water heating subsystem of a high pressure washing system was by using a pressure switch. A pressure switch flips between its xe2x80x9coffxe2x80x9d and xe2x80x9conxe2x80x9d positions depending on whether there is pressure present in the water pipe leading out of the water heater tank. When pressure was present, the pressure switch allowed the burners to operate. When pressure was removed, the pressure switch turned off the burners.
Regulating the burners with a flow switch rather than a pressure switch is another method that is used in the industry. A flow switch senses flow rather than pressure. Thus, while a customer is using the washing system, a flow switch can sense the flow of water through the system and can turn on the burners during this time. When the customer releases the trigger on the washer""s wand, the water flow ceases and the flow switch can be used to turn the burner off.
Many known flow switches in the high-pressure washing system industry are reed-type switches. In such a reed switch, a piston within a water pipe is spring loaded. While water is flowing through the pipe, the water pressure against the piston compresses the spring, causing the piston to be located at a certain position within the pipe. Once the water pressure is relieved, the piston is no longer pressed against the spring, and so the spring decompresses, moving the piston back to its resting position. The piston within the pipe is fitted with a magnet which interacts with a metal reed component of the reed switch. The reed switch sensor is installed exterior to the water pipe, parallel to the piston""s axis of movement. The metal reed switch sensor opens or closes depending on the piston""s position within the pipe.
Such reed switches have their disadvantages. Foremost, to protect the switch, the reed switch is placed in a sealed glass capsule-like container. Glass is needed because of its magnetically neutral properties. The glass container may be housed in a thin brass sleeve for attachment to the water pipe. Of course, the glass container is prone to breakage. In fact, the glass container is sometimes damaged even during shipping. If shipping doesn""t break the glass container, installing the switch can break it. Often, the reed switch within the glass container is attached to the brass sleeve or water pipe with a set screw. If this set screw is overly tightened, the glass container breaks. Even after installation, a reed switch remains prone to breakage from undue vibrations in the water pipe or by carelessness of maintenance workers when working near the switch.
Another disadvantage of the reed switches is the calibration needed during installation. The reed switch within its glass container opens and closes based on a magnetic field from the magnet on the piston within the water pipe. On installation, the reed switch must be positioned very precisely so that the switch will open and close properly. If the switch is not calibrated correctly against the piston""s magnet, the switch will not be able to correctly sense the flow of water through the pipe. Each time the reed switch is replaced, this calibration must be repeated.
A disadvantage to some of the current reed-type switches is the pressure drop associated with using the switch. Some current switches can cause a pressure drop of between 30 and 45 p.s.i. when the flow rate is at 7 gallons per minute. This pressure drop is an inefficiency that makes a washing system utilizing such switches less desirable.
Because reed-type switches have such disadvantages, there have been various attempts to invent a better flow switch. In one area of development, magnets have been used as part of the switching apparatus. For example, U.S. Pat. No. 4,499,347 to Richards (issued on Feb. 12, 1985) discloses a flow indicator mechanism having a hinged plate, flapper valve. A magnet is attached to the end of the flap to activate a switch. As another example, U.S. Pat. No. 4,963,857 to Sackett (issued on Oct. 16, 1990) discloses magnets tripping both reed switches and microswitches. The magnets are placed on a shaft so that they can move along the shaft by the pressure of the flow of fluid.
While these attempts of incorporating magnets in flow switches offer some improvement over the standard reed-type switches, all of these inventions suffer from one or more deficiencies. Some prior magnetic switches utilize complex components to activate the switch mechanism, including small components that must be tooled or machined. Others need many additional components in assembly to monitor fluid flow. With additional moving parts and added complexity, such prior art switches are more susceptible to contamination and operation under extreme conditions. Many of the prior devices also had sensitivity issues concerning the amount of flow and pressure needed to activate them.
It would be desirable to manufacture a switch that alleviates the disadvantages of the current flow switches. It would be desirable to have such a switch not encased in glass or other fragile material so that the switch could be quite dependable and rugged. It would also be desirable to have the switch operate reliably with as few mechanical parts as possible, particularly in the fluid passageway, as those parts are most susceptible to damage. A switch which can self-calibrate or self-align would be quite advantageous, especially if this alignment could be accomplished without a mechanical guide. In addition, it would be advantageous to have a flow switch in which the switching element is compartmentalized out of the fluid flow path. This would eliminate a potential seal breach resulting in switch failure.
The present invention is a in-line flow switch for a high-pressure washing system or other flow-related system. The in-line flow switch can be configured to be normally in the open position and triggered by the flow of water or other fluid through a pipe. Alternatively, the in-line flow switch can be configured to be normally in the closed position, but opened by the flow of water or other fluid through a pipe.
The flow switch includes a housing with an inlet and outlet port. The housing is connected to a pipe system so that fluid flows from the pipe into the inlet port, through the housing, out the outlet port, and continues along the pipe.
Within the housing is a plunger which is sensitive to flow through the housing. A plunger magnet is attached to the plunger. External to the housing is situated a sensor (such as a microswitch) having a sensor magnet attached. The sensor magnet and plunger magnet are configured so they oppose one another. Thus, when flow is absent in the housing, the plunger magnet and thus the plunger are moved away from the sensor magnet. When flow is present in the housing, the repellent magnetic force of the magnets are overcome by the flow and the plunger moves to a position within the chamber and the plunger magnet activates the sensor. The sensor is configured to react to the dual positions of the plunger. In this way, the sensor can indicate when flow is or is not present. In some embodiments, a display unit (such as an LED unit) is also electrically connected to the sensor so that the display unit visually indicates whether there is flow in the housing.
In some advanced embodiments, there is a third magnet, known as the alignment magnet. The alignment magnet is positioned near the housing so that it naturally attracts the plunger magnet. This attraction properly orients the plunger magnet so that it can successfully interact with the sensor magnet and sensor to cause the sensor to open and close as appropriate.
The flow switch assembly advantageously is made up of inexpensive, non-magnetic durable materials, without the need for a reed switch""s use of glass. An advantage of the present invention is that when the flow switch assembly is installed, the calibration procedure needed with prior reed switches is eliminated as the alignment magnet will automatically orient the plunger magnet. The use of the sensor magnet and plunger magnet also allows the flow switch to be built without the need for a spring to move the plunger in the absence of flow.